The present invention relates to a method for suppressing a speed ripple by using a torque compensator based on an activation function. More particularly, the present invention relates to a speed control technology for a motor, in which a torque is compensated and a speed ripple is suppressed based on a speed error of a speed ripple when the speed ripple is generated due to periodic torque ripples synchronized with the angular frequency caused by the measurement error of current, the dead-time, the cogging torque, and variation of the load torque in the motor.
In general, a permanent magnet synchronous motor (PMSM) has the simple structure, high efficiency, high power output and low cost, so the PMSM has been extensively used in various industrial fields, such as robots and household electric appliances.
A proportional controller, a proportional-integral (PI) controller, and a proportional-integral-derivative (PID) controller are used to control the PMSM control system in such a manner that the PMSM control system can be operated according to external commands. The above controllers detect the output of an object to be controlled to allow the object to rapidly follow the command values.
The PID controller according to the related art has performed the control operation through three schemes of 1) limited integrator scheme, 2) conditional integration scheme and 3) tracking back calculation scheme.
For instance, the PID controller performs the feedback control through the PID control until the present RPM of a BLDC motor reaches the target RPM.
FIGS. 1 and 2 are block diagrams showing the structure of the PID controller according to the related art, in which FIG. 1 shows the structure of a general PID speed controller and FIG. 2 shows the structure of a general anti-windup PID speed controller.
That is, as shown in FIG. 1, the PID control is a feedback control to maintain the output to the level of reference voltage based on the error between the control parameter and reference input. The P (proportional) control makes a control signal by multiplying the proper proportional constant gain by the speed error ωerr between the reference speed ωref and the actual speed ωact, the I (proportional integral) control is achieved by parallel connecting the integral control, which makes the control signal by integrating the error signals, to the proportional control, and the D (proportional derivative) control is achieved by parallel connecting the derivative control, which makes the control signal by differentiating the error signals, to the proportional control.
Meanwhile, Korean Unexamined Patent Publication No. 2011-0094946 (publication date: Aug. 24, 2011) discloses a PID controller including a driver operating in a linear region or a saturate region, a proportional controller performing a proportional operation with respect to the error between a reference value and an output value of a plant, a differential controller performing a differential operation with respect to the error, an integral controller performing an integral operation with respect to the error when the driver is operated in the linear region, an integral state predictor predicting the integral state under the normal sate of the integral controller, and an integral state initializing loop allowing the initial state of the integral controller to have the integral state value of the linear region before the driver enters the linear region by using the integral state under the normal state of the integral controller.
In addition, Korean Unexamined Patent Publication No. 1999-0084680 (publication date: Dec. 6, 1999) discloses an anti-windup PID controller, which removes the accumulated errors when the value of the accumulated errors deviates from the reference range as the integral values of a proportional integral controller are accumulated, thereby precisely controlling air pressure within a predetermined range and constantly maintaining air flux in a clean room.
Further, Korean Unexamined Patent Publication No. 2011-0014874 (publication date: Feb. 14, 2011) discloses a control system for a permanent magnet synchronous motor, which includes a position estimation part for estimating a position of a rotor of a motor, a current measurement part for measuring current according to voltage applied to the motor, a position error calculation part for calculating a position error between an actual rotor position and an estimated rotor position by using the measured current, and a position correction part for correcting the position of the rotor by using the calculated position error.
However, the above conventional technologies fail to disclose the torque compensation and the suppression of the speed ripple.